One example of exhaust gas purification device that captures the particulate matter (PM: particulate matter: referred to as PM, hereinafter) emitted from a diesel engine by a filter which is called a diesel particulate filter (DPF: referred to as DPF, hereinafter) is seen in a continuous regeneration device type DPF device.
In the continuous regeneration device, when the exhaust gas temperature is equal to or more than approximately 350° C., PM captured by DPF burns continuously to be purified and DPF is regenerated by itself. However, when the exhaust gas temperature is low in a case of low speed with low load, catalyst is not activated due to catalyst temperature drop and thereby it becomes difficult to perform self-regeneration of DPF through oxidation of PM. Owing to this, clogging is promoted due to accumulation of PM in the DPF, resulting in a problem of back pressure increase caused by the clogging.
Thereby when the clogging amount of the PM in the DPF surpasses a predetermined value (threshold), exhaust gas temperature is forcibly raised by means of multistage delay injection (multi-injection) in a cylinder (in a tube) or after injection (post injection) and the like to carry out forced regeneration which removes captured PM forcibly through combustion. In this forced regeneration, HC (hydrocarbon) supplied in the exhaust gas through post injection and the like is burnt by oxidation catalyst disposed upstream of the DPF or by DPF-supported oxidation catalyst, the oxidation reaction heat of which is utilized to raise the exhaust gas temperature of the DPF entrance or the filter surface of the DPF. Owing to this, the DPF temperature is raised above the combustion temperature of PM accumulated in the DPF so as to perform combustion removal of the PM.
There are two cases in this forced regeneration, one is manual and the other is automatic. In a case of manual regeneration, when the clogging of the DPF surpasses the predetermined amount, a warning is given to the driver and the driver who receives the warning pushes a button to start the forced regeneration to perform it. On the other hand, in a case of automatic, when the clogging of the DPF surpasses a predetermined amount, no warning is given to the driver, but the forced regeneration is performed automatically even during driving.
Among the forced regenerations, there is a forced regeneration for a long time idling which is carried out when idling state is sustained longer than predetermined time. In vehicles specially equipped with PTO device, however, such as a mobile mixer, a truck crane, a fire engine and so on, when forced regeneration is performed in a state where the PTO device is in operation, variation of rotation tends to occur since the delay combustion is an unstable combustion. In addition, injection timing varies significantly depending on load, which causes a problem of effect of engine speed variation.
Concerning this problem, in prior art, the forced regeneration of the DPF has been forbidden in an idling state and when the PTO device is in operation. For example, as described in Japanese Patent Application Kokai publication No. 2004-150417, in a vehicle specially equipped that is arranged to be able to take out engine power for driving auxiliary unit via PTO device in an idling state, as for an exhaust gas purification device which performs forced regeneration control through raising engine speed in a case where forced regeneration is required in an idling state, such a exhaust gas purification device has been proposed that a regeneration control command is arranged not to be output for performing forced regeneration through such as an additional post-injection or an increase of rotation in a condition where the PTO device is in operation, so as to avoid sudden change of engine operating condition or malfunction of an auxiliary unit, which tend to occur when forced regeneration is performed in a condition where the PTO device is in operating state.
In a similar exhaust emission purification device, for example, as described in Japanese Patent Application Kokai publication No. 2005-139944, such an exhaust gas purification device has been proposed that, placing great importance on the practical performance of the PTO device, temperature rise control command is arranged not to be output from the control device exclusively when the PTO switch is on and operational input is detected for an auxiliary unit via such as a lever specially equipped for external acceleration.
However, in vehicles specially equipped, large amount of PM is accumulated in DPF due to the load of special equipment in shorter time than standard vehicle that has no special equipment. Therefore, if forced regeneration in long time idling operation is forbidden when PTO device is in operation, clogging of DPF is occurred and back pressure is raised excessively causing a problem of engine running malfunction. That is, in a case where low and middle load operation is repeatedly performed as the case where long time idling is in operation while PTO device is in operation, forced regeneration can not be performed despite that PM is accumulated in short time. Owing to this, there is a risk of excessive amount of PM is accumulated in the DPF. If the DPF is reused through forced regeneration so that the PM accumulation is removed, PTO operation has to be suspended, which causes a problem of deterioration of working efficiency.    Patent Document 1: Japanese Patent Application Kokai publication No. 2004-150417    Patent Document 2: Japanese Patent Application Kokai publication No. 2005-139944